Electrical contact



Patented Oct. 13, 1942 ELECTRICAL CONTACT Wallace T. Allen, Royal Oak, Mich, assignor to Square D Company, Detroit, Mich., a corpora tion of Michigan No Drawing. Application August 3, 1940, Serial N0. 351,186

'7 Claims.

This invention relates to electrical contacts,

I particularly for circuit breakers opening automechanisms wherein the contacts separate automatically under the action of a spring bias upon the occurrence of a current overload through a current responsive device. In this operation, for the correct functioning of the breaker, it is necessary that the contacts be substantially non-welding so that they will not stick together and it is further necessary that the contact shall be relatively refractory so that it will not be dissipated by the action of the intense arc occurring on the interruption of short circuit currents. It is further necessary that the contact resistance between the cooperating contacts be kept below a value which would result in excessive heating at the contacts.

For the non-welding and arc resisting characteristics, it has been found that cooperating contacts comprised of a material having its principal base formed of a mixture of silver with tungsten, molybdenum or other refractory metal are satisfactory. However, it has been found in certain cases that the contact resistance of such contacts tends to increase beyond the limiting value so that their operation and the calibration of thermally released tripping elements is adversely affected. It is the object of this invention to provide a circuit breaker contact having a silver tungsten or silver molybdenum base whose contact resistance will be maintained within allowable values without adverse effect upon the non-welding and arc resisting characteristics.

Other objects and features of this invention will be readily apparent to those skilled in the art from the following specification:

The contacts, according to this invention, may be formed of a base material of silver and tungsten or molybdenum or other refractory metal in which the contacts may be formed either from a mixture of the powdered metals pressed into solid contact form or in which the tungsten or molybdenum in porous solid form may be impregnated with the silver, both of these methods of formation being well known in the art and forming no part of the present invention. The proportions may be varied greatly and, for example only, the materials may be present in proportions of 35% to 55% of silver and 45% to 65% of tungsten or molybdenum. These contacts may also contain a minor percentage of carbon.

According to the present invention, the contacts so formed are provided with a thin coating of silver on at least the contact face, although the coating may obviously be applied to the entire contact if desired. This coating will be of a thickness suilicient to permit it to be retained under the action of interrupting the current but thin enough so that beads sufiicient to cause the contacts to be welded together will not occur. The permissible thickness of the coating will be dependent to a great extent upon the circuit breaker mechanism and the strength of the operating springs and it is, of course, de-

sired to make this coating as thick as possible without adversely afiecting the non-welding characteristics of the contacts. In certain types of commercial breakers, it has been found that a coating of about .002 would be the maximum which would maintain the non-welding characteristics of the coatings, and this coating was found to maintain itself under the circuit interrupting action and to prevent the increase in contact resistance. However, in larger and heavier breakers, it is found that a coating of as much as .010" could be used and the non-welding characteristic retained.

By means of this invention, an important disadvantage to the use of refractory non-welding contacts has been obviated without injuring their refractory and non-welding characteristics.

While certain preferred embodiments of this invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

1. An electrical contact comprising a refractory substantially non-welding base and a protective coating on at least the contacting surface of said contact exterior to said base, said coating being of a high conductivity, normally weldable material and of a high conductivity, normally weldable material and of suflicient thickness to substantially maintain itself under the circuit interrupting operation, but thin enough to substantially prevent adverse effect upon the non-welding characteristics of the contact.

2. An electrical contact comprised of silver and a refractory metal of the group tungsten and molybdenum having a thin protective exterior coating upon at least the contacting surface thereof, said coating being of a high conductivity, normally weldable material but sufficiently thin so that it will not adversely affect the non-weld ing characteristics of the contact.

3. An electrical contact comprised of silver and a refractory metal of the group tungsten and molybdenum having a thin exterior coating of silver upon at least the contacting surface thereof, said coating being sufiiciently thin so as not to interfere with the non-welding characteristics of the contact.

4. An electrical contact comprised of silver and a refractory metal of the group tungsten and molybdenum having an exterior coating of silver upon at least the contactsurface thereof, said coating having a thickness between .002" and .010".

5. An electrical contact comprised of a pressed powdered mixture of 35% to'55% silver and 45% to 65% 'of a refractory metal of the group tungsten and molybdenum, having a protective exterior coating on at least the contacting surface thereof, said coating being of a high conductivity, normally weldable material and sum-- Patent No. 2,299,000.

HALIAOE r. ALLEN.

ciently thick to maintain itself under the circuit interrupting action, but sufliciently thin so as not to adversely affect the non-welding-characteristics of the contact. w

6. An electrical contact comprised of a refractory metal of the group tungsten and molybdenum impregnated with silver in proportions of to 55% silver and to 65% of the refractory metal having a protective exterior coating on at least the contacting surface thereof, said coating being of a high conductivity, normally weldable material and sufliciently thick to maintain itself under the circuit interrupting action, but suiilciently thin so as not to adversely affect the non-welding characteristics of the contacts.

7. An electrical contact comprised of silver and arefractory metal of the group timgsten and molybdenum in the proportion of substantially 35% to of silver and 45% to'65% of the refractory metal, having an exterior coating of substantially .002" to .010" of silver on at least the contacting surface thereof.

wants or: '1'. ALLEN.

CERTIFICATE OF CORRECTiON October 15,- 19i 2.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 1, second column, lines and 11.7, claim 1, strike out "a high conductivity, normally weldable material and of" and that the said Letters Patent should be read with this correction therein that the same may conform to the rec- 0rd of. the case in the Patent ,Office. I

Signed and sealed this 24th day of November, A. D. 1914.2.

Henry Van ,Arsdale (Se l) acting commissioner of Patents.-

cnnnmcam w oomcnou.

Patent no. 2,299,000. octeber 15,- 19!;2.

WALLACE 1'. ALLEN.

It is hereby certified that error appears: the printed apecification of the above numbered patent requiring correction as follows: Page 1 sec-- ond cdlfimn, lines 14.6 and k7, claim 1, strike out "a high conductivity,

normally weldable material and 31" add that the said Letters Patent aheuld be read with this correction therein that the same may conform to the rec- 0rd of the case in the Patent ,Office.

Signed and sealed this Zhth day of November, A. D. 19l|.2.

Henry Van Arsda Ie (seal) Acting Commissioner of Patents. 

